1. Field of the Invention
This invention relates to fuel filters and, more particularly, to a replaceable, diesel fuel, filter element that actuates a standpipe flow element in a filter housing.
2. Background Art
As shown in FIG. 1 herein, U.S. Pat. No. 5,458,767 describes a filter assembly 1 including a threaded cover 10, a housing 11, and a replaceable filter element 12. The filter element 12 includes an upper endcap 14, to which a cylindrical filter media 16 is attached. The upper endcap 14 attaches to the cover 10 via a pair of opposing latching fingers 18 removably received in engaging recesses 20 formed on the cover 10. A lower endcap 22 includes a central opening 23 receiving upwardly therethrough a standpipe 24 which houses a spring-biased movable flow element 26.
A downwardly extending hollow projection 28 is formed centrally on the upper endcap 14 and has the following function. In a normal operation, when the cover 10 and the element 12 are attached, a projection 32 formed on the underside of the cover 10 is received in the hollow projection 28. When this combination is screwed onto the filter housing 11, the projection 28 pushes down against the spring-biased flow element 26, thereby putting cavities 34 in the flow element 26 and openings 36 in the standpipe 24 in fluid communication. This alignment allows fluid to flow between an area 38 inside the media 16 adjacent the standpipe 24, to the interior of the standpipe 24, and out an outlet port 42 (not shown).
The element 12 must be replaced after its useful life. To do this, the cover 10 is unscrewed from the housing 11 (which takes the connected filter element 12 with it), whereupon the projection 28 releases its force on the biased flow element 26, which closes under the pressure of a spring 40, and cuts off the above-described fluid communication. The used element 12 is then removed from the cover 10 and discarded, and a new replacement filter element 12 is attached to the cover 10, which is again screwed on the housing 11 for use.
A drawback to this structure is that the projection 28 formed in the upper endcap 14 is difficult to reliably form in a traditional one piece sheet metal endcap. That is, the metal has to be drawn significantly in order to form the elongated projection 28, which is a difficult manufacturing step, and may cause a weak projection 28. Also, flexible latching fingers 18 are required. From a practical point of view, it is necessary to form this entire upper endcap 14 from plastic. Of course, it is then necessary to choose a plastic that is compatible with the fluid that is being filtered. It is also necessary to make a mold for producing the endcap. Further, significant plastic material is used for the entire upper endcap, even though only the projection and latches may require same. These considerations raise the costs of producing the filter relative to one that has a traditional metal upper endcap.
Further, this design generally requires that the cover and the upper endcap be compatible, i.e., that the projection 32 on the cover 10 reliably seat in the projection 28 on the upper end plate 14. To ensure this arrangement, it appears best to require the cover 10 to receive the filter element 12 thereon. Accordingly, this patent describes the separate arrangement of spring fingers 18 that are removably received by recesses 20 on the cover. This type of design, then, requires that the manufacturing parameters for one part be dictated by the parameters of another part. Defects in one during manufacture can affect the other, which can lead to excessive waste. Also, a needed design change in one may necessitate a design change in another. These considerations again may increase costs and limit design flexibility.